1. Field of the Invention
The present invention relates to a method for mounting a scale having a measuring graduation on a support, as well as to an arrangement with a support and with a scale which is releasably, but yet stably, fastened thereon.
2. Discussion of Related Art
For measuring the relative position of two machine elements, a scale must be fastened on one of the machine elements and a scanning unit on the other one of machine elements which are movable in relation to each other. A measuring graduation of the scale is scanned in the course of position measurement.
For a highly accurate position measurement it is necessary for the scale to be maintained stably and free from drifting on the support. A high degree of stability and freedom from drifting in the nano range and sub-nano range requires an extremely short force path, which should be restricted to the contact face, if possible, and should not include the entire thickness of the scale.
For example, a short force path, if possible restricted to the contact face, can be achieved by bonding (atomic van der Waals forces). In this case scales made of glass or glass-ceramic material with negligible coefficients of expansion are preferably employed. These scales can be easily worked, so that here bonding at optically polished counter-faces is customary, such as described in DE 101 53 147 A1. Bonding is a fastening method for scales which is very drift resistant. However, with bonding there is the danger that the scale peels off or is partially loosened. Therefore the outer edges of a bonded scale can be unstable if alternating loads occur at the edge (for example because of acceleration or temperature variations), and these edge zones therefore repeatedly peel off and are bonded again. Furthermore, a bonded scale is very difficult to remove from a support, and therefore an exchange of a damaged scale is possible only with difficulty.
A further known method for mounting a scale on a support is gluing in the area of the contact face. Depending on the type of the adhesive and the thickness of the glued place, distortions between the support and the scale because of shrinking processes can occur, which lead to non-reproducible linear errors in the scale. The shrinking processes in the adhesive are induced, for example, by the aging of the adhesive or by changes in temperature and humidity. Glued-on scales are also very difficult to remove; they can hardly be taken off without leaving a residue.